Localization and induced expression of fusion genes in the rat lung

Liposome-mediated gene transfer is useful for DNA transfection into cells in culture. We wondered whether this method could be used to introduce new DNA into the intact lung. Fusion genes containing either the Rous sarcoma virus (RSV) promoter or the mouse mammary tumor virus (MMTV) promoter (which contains glucocorticoid response elements) were linked to the bacterial gene chloramphenicol acetyltransferase (CAT), an enzyme not present in mammalian cells. Plasmids containing the RSV-CAT fusion gene were mixed with cationic liposomes (Lipofectin; BRL, Inc., Grand Island, NY), and single doses were instilled into the cervical trachea of anesthetized rats. Control rats received either liposomes or plasmid. After 24, 48, and 72 h, lungs were perfused free of blood, homogenized, and analyzed for CAT enzyme activity. Liver and kidney tissue were also obtained. We found that rats given either intratracheal liposomes or plasmid had no detectable CAT activity. By contrast, 24 h after instillation of lipid:DNA complexes, lung CAT expression remained elevated for the next 48 h but was barely detectable in liver or kidney. In another group of rats, MMTV-CAT:liposome complexes were instilled intratracheally and then the rats were injected with either dexamethasone or saline. We found that the dexamethasone-treated rats had a 5- to 10-fold higher level of lung CAT expression at 24 and 48 h than the saline-treated controls had; liver and kidney CAT levels were negligible in both groups. Dexamethasone treatment did not increase RSV-CAT expression, indicating that the dexamethasone effect on MMTV-CAT expression was related to the presence of the MMTV promoter.